Category Archives: Microphones

Polyribbon Photos

My good friend Sandy Andrews happens to be a commercial photographer in Columbia, SC, so when I travelled there for the IPMS Nationals, I brought the Polyribbon with me and we headed over to his studio. These shots are the result. Sandy does catalog work for some very high-profile clients, so he’s got the chops (and the equipment, and the space) to shoot some really nice images. Hopefully you’ll see these in Mix Magazine someday!

While this looks like a vintage mic, everything in it is brand new. Les Watts, the designer, is a little bit neurotic when it comes to accuracy and quality… everything on this mic is executed with tolerances that are extremely close, which makes building these very time consuming and expensive. The banding around the headbasket is hand-filed brass that is then nickel-plated, the edges of the grille are all soldered. The frame that holds the magnets are assembled with dowel pins instead of screws, since screws have microscopic gaps that affect the magnetic reluctance of the frame. The wrinkle paint finish on the body is a custom formulation that Les had made just for this mic.

This mic has plain knobs because Les had trouble finding a laser engraver who could maintain the proper accuracy. Since each knob has to be handmade, a screw-up by the engraver would cost hours of work, so they have to be extremely careful. We’ve since located a supplier, so the new mics will have knobs with laser engraved and infilled legends. A simple silkscreened legend is much easier to make and looks the same at first, but these rub off after a few years. Les builds these with an expected lifespan in excess of fifty years, and all materials are selected for longevity.

These mics really need to be seen- and heard- to be appreciated. If you’re interested in acquiring one for your studio, contact me for a demonstration!

_5713_desatbg_5717_desatbg

Watts Polyribbon At Work

Here’s a link to a project that I worked on recently. The band is called Spinster… they’re three sisters with classical music training. One lives on the west coast, one in Chattanooga, and one in Costa Rica, so they don’t get to play very often. We recorded a series of three songs this summer, they’ll eventually be posted on YouTube

We set it up as a live multitrack recording with no overdubs, so it’s very much a live performance video.  It’s also the first chance that I got to use the Polyribbon. I used it on lead vocalsfor two songs… very smooth. And just to change things up a bit, we tried it on the upright bass for one song, which gave a teriffic sound. No EQ was used on the Polyribbon signal.

Recorded on the Sound Devices 664. It was mixed using the Harrison Mixbus 32C using Universal’s EMT 140 plate reverb on the vocals. Instruments are pretty much dry. Noise reduction and mastering via Izotope RX Pro and Adobe Soundbooth.

Hopefully I can get them in the studio this summer for an album. Enjoy!

 

dsc_1503dsc_1516dsc_1523

A Ribbon Microphone- Design 001, Rev A

Since I have to give away the Austin Ribbon Mic that I built, I decided that I wanted one of my own. I purchased raw materials for four more ribbon mics and have been working diligently on another mic. It isn’t completed yet, but I’ve done enough (and it looks good enough) that I can show off some preliminary photos.

My progress so far on ribbon mic no. 2, which incorporates a large number of design changes from the previous mic.

This microphone is similar to the Austin ribbon, but it’s a completely new design inside. The body style is similar, and I’m using a similar motor frame of clear acrylic plastic with drilled vent holes as a frame for the motor, but that’s where the similarity ends.

The Austin mic sounds great, but my outboard preamps are… well… let’s just say they aren’t top-of-the-line models. (Except for my lovely pair of VP26 pres from Classic Audio Products of Illinois, but I don’t have a Lunchbox yet to mount them in. I’ll get them racked one of these days, but the studio needs to generate some income first.)

So as a result of my gear, I’m having to crank the preamps up a good bit on the Austin mic. It sounds great on a source like an acoustic guitar, but for voice it requires a super clean preamp. (The Crest preamp that I recently purchased is a significant improvement.) This new design is an attempt to increase the output a little so that I can get a better signal with more common equipment.

My redesigned ribbon motor frame with magnets in place. A central groove is milled in the plastic for positioning the ribbon. The magnet spacer is just a piece of 4mm aluminum.

I’ve redesigned the motor frame using magnets that are slightly larger at 5mm x 10mm, and a ribbon that is slightly narrower, about 3.5mm. It’s counterintuitive, but narrower ribbons have a higher output. I’m using a 2.5 micron aluminum ribbon foil. The plastic frame is machined with a slot down the middle to hold the ribbon, and a pair a milled aluminum clamps to hold the ribbon in place. I didn’t want to use copper here because of galvanic reaction concerns. Everything is held in place by 4-40 capscrews, which are magnetic & will probably be a pain in the ass to install, but we’ll see. I’m waiting until most of the work is completed before I install the magnets and the ribbon, since the magnets will attract bits of ferrous crud in handling & the ribbon is so very fragile. That’s why they aren’t in place in the photo above.

The frame installed on the motor mounting tube. The ribbon clamps have been machined and are in place. I’ll probably secure the wiring with a dab of glue once the ribbon is installed.

Another difference is in the motor mount. I’ve built a secondary can that slides inside the mic body from a small piece of galvanized fence tube with a fender washer silver soldered to the top. This will shield the transformer almost as well as a Mu-metal can, and it makes a sort-of “mic-within-a-mic.” This same type of construction is used with great results on the Electro-Voice RE50 reporter’s mic, one of my favorites. This sub-assembly is isolated from the outer shell of the mic with a wrap of foam. This will be of limited benefit, since a ribbon mic is never handheld except when used as a prop in music videos. But I did want some way to take the mic apart and put it back together as a single unit… the Austin design has the motor pressed against the mic body with strips of neoprene foam. It works well, but isn’t ideally suited to taking the mic apart. I expect to do that a bit more with this mic, as I experiment with things like silks around the ribbon or waffle-plate resonators.

I’m calling this one Revision A, since I redesigned & rebuilt the mount to correct a grounding problem. I’m already working on Revision B, which will be largely similar except for the ribbon clamps and  more space at the bottom of the frame for mounting the motor with screws. (Revision A’s mount is secured with glue.) I’ve got some other ideas to try with magnet sizes and frame designs, but I need to give these an extensive listening test first.

I’m still waiting on a few parts… the transformer and the XLR, mainly… but I hope to have this project finished soon, and I’m anxious to hear the results. In the meantime, I’ve started milling parts for another one.

The semi-completed shell. I still need to machine the brass cap at the bottom and mount the XLR connector. Overall length is just about six inches.

The cost for this project is fairly high, mainly due to the amount of time that is spent in construction. If you add in the cost of the machine tools, the cost goes from fairly high to astronomical. I’m using a benchtop drill press, a 7×10 Chinese lathe and Taig milling machine to make these. All three have been essential for various parts of the work. While it would be theoretically possible to build a mic with hand tools, it is a lot easier to get good-looking results in less time with some heavy machinery. (If you lack the tools, Rick Wilkinson’s Austin ribbon mic kit is highly recommended, see my previous post.) And actually, my setup is pretty minimal… I could use a larger lathe & a CNC mill for faster and better results… but now we’re talking about an investment that would require going into business as a mic manufacturer, which isn’t my intent. These are experiments. I’ll probably make a few available for sale at some point, just to recoup some of the cost of the parts. And I expect the price on them to be rather high, just because they take so very long to make. But these are primarily built for my own satisfaction. It won’t hurt the resume, either.

I owe a great debt to Rick Wilkinson and Les Watts (former mic designer with Shure and EV) for teaching me a large majority of what I know about building ribbon mics. Their help is very much appreciated.

UPDATE: I’ve very nearly completed this mic… I recut an existing XLR connector on my lathe, so now it fits the microphone. The magnets were fitted to the frame, and I mounted a 2.5 micron ribbon yesterday. I’m guessing it’s about 3.6 mm wide. It’s a nice, tight fit. The ferrous capscrews were a pain in the ass, but not impossible to deal with.

The ribbon motor completed, with magnets and ribbon installed. Using 2.5 micron ribbon material is much easier than signwriters leaf, though it’s still not a simple process to install.

Now I’m just waiting on the transformers to arrive. These will be a special custom-wound ribbon transformer that should meet or exceed specifications from the usual suppliers. Unfortunately, it probably won’t arrive in time for the DIY seminar… I was hoping to have this working before then.

This mic comes with a custom walnut mic box that I had built by a local cabinetmaker. Nothing on this mic is sourced from Chinese suppliers… that sort of thing is easy enough to get from just about anywhere these days. If nothing else, this mic will be different from the common stuff that is so prevalent these days.

UPDATED UPDATE: When I went to use this mic recently, I discovered that the glue had failed on one of the magnets and it had separated from the frame, bringing the two together and turning the carefully-placed ribbon into aluminum dust. So while this is an easy-to-build example of how ribbon mics work, it isn’t the best design in terms of longevity.

My new design incorporates a steel frame rather than plastic. This is slightly better from a magnetic perspective, and it’s naturally stronger for threads, etc. I’m thinking of trying a frame made from small pieces of 1/4″ square steel. Machining from solid would be a possibility, or I could even get crazy and go to the blacksmith shop and forge something… I was formerly a full time blacksmith and still have access to some large and heavy tooling. And I’m pretty sure that nobody else is hot forging their ribbon mic parts.

But the key design element will be a small notch to hold the magnets apart. I should have done this before, as it could be incorporated into my earlier frame design. It’s yet another thing to put on my long list of projects.

The finished mic in its custom-built, handmade walnut box.

Austin Ribbon Mic Completed

The completed Austin ribbon mic. This one will be given away at the Producer’s and Engineer’s Summit at Welcome To 1979 in Nashville, coming up in November.

Here’s a look at my Austin ribbon mic, I completed it yesterday. Building this mic certainly was actually really easy, except for one part… installing the ribbon in the frame. I had to do this several times… six, to be exact. I  had various problems. One, for example, didn’t show it’s ugly head until I’d completed an installation… tiny tears all along the edge of the ribbon. I learned they were caused by the ruler I was using, which had a cork backing that was set slightly behind the ruler’s edge. This small unsupported space allowed the foil room to stress and tear. I corrected this by using a length of rectangular aluminum as a straightedge, this pressed down on the foil right at the cutting edge.

Another problem I had was corrugating the ribbon. I was trying to protect the ribbon by corrugating it with the release paper on the top and bottom, but doing so a) causes the ribbon to curl up, and b) makes the corrugations shallower. If the ribbon isn’t sufficiently corrugated, it is extremely difficult to get it tensioned properly. The tension is important… the ribbon can neither sag in the frame, nor should it be too tight. I had the latter problem, and the ribbon developed a longitudinal curl, so scratch that ribbon.

But thanks in no small part to Rick’s patient support via several emails, I finally got one in. It wasn’t perfect… it could be centered just a hair better… but it looked ok, so I closed it up and finished the mic.

And considering everything, it sounds quite lovely. The last time I used a ribbon mic was 25 years ago, when I did my thesis recording using a pair of RCA TK77’s that the university owned, so I don’t have much of a frame of reference, but it seems to have a nicely balanced frequency response. From what I understand, construction errors show up as poor highs or lows. I don’t have a frequency analyzer set up yet so I can’t give any numbers, but my subjective analysis says “nice.” Now, like all ribbons, the output is rather low, and I did my testing using a rather crappy mic preamp. On voice, one has to crank the gain up quite a bit, and this gave me a lot of preamp noise. For someone who is a low talker, this wouldn’t work. But I got a rather useable level on my acoustic guitar.

Again, I can recommend Rick’s kit quite highly, especially if you’ve never built a mic before. He’s done everything that can be done to insure a good outcome, and the one I built certainly worked out well. That’s not to say it’s simple… you need patience, and good, steady hands will help as well. But I’ve already got parts here to build four more for myself!

The Austin Ribbon Mic

I recently received an Austin Ribbon mic kit from Rick Wilkinson (Rickshaw Records) out in California. Unfortunately, I can’t say I’m the proud owner… this mic is going to be built and given away as a door prize at the DIY panel at the Producers and Engineers Summit at Welcome To 1979 in November.

I haven’t finished the build yet, so I can’t give a complete review of the mic, but I can make some comments about the kit and the resources that come with it. Building a ribbon mic is not that complex- IN THEORY. It’s just a thin metal ribbon suspended between two magnets. There isn’t much electronic inside the mic, just a transformer. The design has been around since the 30’s.

The theory is simple. But like most things, it’s the Devil in the details. You can find articles and instruction on the web for free. And that’s what I started to do years ago. I got halfway through the project and shelved it… there wasn’t enough detail for me to be successful.

Or you can spend some money and increase your chances. Rick sells plans for ten bucks, or his ribbon kit for $275 with a Cinemag transformer. (There is a less expensive version with a stock transformer, and I understand the stock transformer is exceptionally high quality. It’s sold out right now, but should be available again shortly) Rick sent me a kit with a Cinemag transformer, so that’s the version I’m reviewing here.

The kit itself is extremely well done. The mic tube is powder coated brass, 1 1/2″ diameter, and exactly machined. All the holes are already drilled, so you don’t need a drill press. The motor frame (a critical part) is a machined piece of plastic. The fit was perfect. I especially liked his design… I designed my own once, and it was a cumbersome mess. Ricks is elegant, simple, strong, and works well. (some folks claim that metal frames are superior. Perhaps they are… I’m not sure… but I think that at least part of the reason behind this claim is that’s what is available from China.)

The greatest value for me, though, is Rick’s instructional materials. When you buy a kit (or his plans), he sends you a link where you can download  PDF instruction manual and several videos where he goes through the process of building a mic. These videos are really helpful, especially when it comes to corrugating and installing the ribbon.

Commercial mics use ribbons that are anywhere from 5 microns to 1.8 microns thick. The ribbon material that Rick supplies is about 0.8 microns. (Thinner ribbons increase high-freq sensitivity.) This is similar to “imitation silver” guilding leaf, it’s readily available on the internet. I’ve bought some from Hobby Lobby before and tried to cut a ribbon from it. I can say without hesitation that it ain’t easy. But that’s the beauty of these videos. Once you see someone doing it, you understand the method better… much better than just reading about it. And you can see that it is possible to make a well-functioning ribbon from scratch, but understand that it’ll take some practice. Even breathing can cause a cut ribbon to fly off your bench. So be ready to make several practice ribbons before you get one correctly made and mounted in your mic frame. And if you just can’t get it, there is an internet source for commercial ribbon foil now. A company called Lebow sells pure aluminum foil in a variety of thicknesses, including 1.8 and 2.5 microns. This would be vastly easier to handle, but it’s also vastly more expensive at $25/sheet. (There may be other sources as well, but this was the only one that I could find. I ordered two sheets to use in my own mics, but they aren’t in yet.)

Ribbon-making details is a big advantage of his instructions, but it isn’t the only one. For example, I learned that you can use a brass footrail cap on the bottom of your mic to hold the XLR connector. These things are nice, solid castings, and if you shop around, you can find them at about $5 apiece. (I wish I’d thought of that.) Circular Switchcraft connectors fit well in these caps.  This would be a good solution for any tubular-bodied homebuilt mic.

The videos do have a slight downside. You have to remember that Rick has built a lot of mics, so some of the things he does in the videos look easier than they will be to folks like you or I. It’s really difficult to explain the things that practice teaches you. But I’m pretty sure that I’ll have a working ribbon mic once the dust settles… I’ll keep you posted.

UPDATE: I finally got up the nerve to install the ribbon today. It worked on the second try, which really isn’t bad. I’m pretty sure that my success with this is pretty much due to Rick’s instruction. Like I said previously, I’ve tried this before and failed miserably. Seeing it done (in a video) makes all the difference.

A just-placed ribbon in the motor frame. This job requires lots of patience, but it can be done.

That is not to say, however, that it was easy. The foil is the definition of flimsy… if it were any thinner I think it’d fly off my bench because of the rotation of the earth. Using the more expensive 2.5 micron foil should be easier (though I expect still no picnic), and that’s what I’m planning for my own ribbon motor frames. (I figured this one should be made as a stock kit, in order to give a fair review.) There will be some slight differences, like slightly thicker magnets… I’m still in the design and prototype phase. But if they work, it’ll be fun to try some design variations like waffle plates (resonators) and silks.

More Mic Mods- the ADK SC-2

Because of my posts about modifying microphones, I recently received an invitation to visit a proper mic designer. Les Watts is an engineer who worked  for some VERY prominent microphone companies… I’m fairly certain that at least one of them is in your locker right now.

Les lives about a three-hour drive from me, so I went by for a short visit recently. It was, of course, extremely educational. I brought along a pair of mics that I had doctored, and we tested them using his calibrated setup.

The ADK SC-2 small-diaphragm condenser microphone. The stock mic is on top, the modified capsule is shown on the bottom.

One of the things that I learned… or rather confirmed… on my trip is that real microphone design is a very slippery fish. A microphone is a true “complex system…” one small change affects a whole host of other factors. The mod that I did (not so much a design as a “I-wonder-what-will-happen-if-I-do-this” sort of affair) was to cut away the area in front of the mic diaphragm, leaving the area more open and less restricted by the grille and metal in front of the diaphragm. It turns out that the “cup” shape that is created by the area that I cut away forms a high-frequency resonator, which I’ve essentially removed. Sometimes this  is a good thing, sometimes not.

The ADK capsule shell disassembled for modification. As you can see, a small-diaphragm capsule is a fairly simple affair with just a few parts. An important part that you can’t see is the spacer ring that lies between the diaphragm and the backplate. It’s a simple washer made from thin mylar film that looks much like diaphragm material… about 6 microns thick.

Assembling the modified SC-2 capsule. Any dust trapped between the diaphragm and backplate will ruin the capsule. It took a few tries.

Consider the following two mic capsules. These are for some ADK SC-2 small-diaphragm condensers that I have. I had an extra pair of dead capsules, so I figured I could play around with these without much risk. (I did get them working again) The only change was removing the cage at the front of the diaphragm, lowering the height of the sides to about 2mm, giving the edges a gentle radius, and using a finer brass screen in front.

I did a quick recording of both modified and unmodified capsules. On guitar, I really couldn’t tell much difference at all. But Les’ test rig tells a different story. Take a look at the following response curves:

First off, you should ignore the huge rise below 200 Hz, which is due to proximity effect of the test setup. What I found interesting was the rise in response of the stock capsule centered around 8kHz. Les told me this is a pretty typical Chinese mic response. Looking at the lower of the two curves, we see that modifying the headshell does even out this rise, and gets us a slightly extended high end response…  but it also introduces a pretty deep notch at around 6kHz. This notch is present in the unmodified capsule too, but to a lesser degree. This could be why the capsule shell was designed the way it was.

Another take-home lesson from my trip is the need for a better testing setup at my studio. Remember, on guitar I could make out very little difference in the two mics. (I don’t have golden ears, but I have done a lot of listening.) Perhaps another recording of something with more transients, like a snare, might be more revealing. Again, according to Les, notches in a response of this sort are very difficult for the average person to identify in listening tests. What I could really use is a setup that’s similar to his.

Les uses ARTA software, which is available as a download. His calibration mic is an extremely expensive calibrated B&K, and his loudspeaker (for generating the test tones) is custom-built. It might be possible to get a similar setup at my studio using some equipment that I already have. It won’t have the accuracy that Les’ system does, but I believe I can get something put together that will show the relative changes of a modified vs unmodified capsule. I’ll need a few things, like a Windows computer… I’ve been a Mac guy for many, many years. (Our first Mac II at the recording studio gave us a HUGE advantage, enabling us to design several cassette and CD releases in-house. Back then, graphics ability was a big deal that only Mac folks could do… nowadays, not so much!)

So I’m currently on the hunt for another inexpensive computer (this will be #4) that I can use with ARTA as a dedicated test machine. My son’s old Dell doesn’t seem to want to generate any video, but I may yet be able to get that one going. If not, it’s off to the thrift store for some computer shopping.

I’ll also need a calibration mic and a speaker. The mic might not be too bad, and I may be able to borrow or beg this one. The speaker will be a little harder, though I do have a pair of KRK5s that might at least get me started.

Lots more to come… stay tuned!

Small diaphragm Condenser Modification Results

Last week I sent the small-diaphragm condenser mics from the post below to a friend in Nashville, John Billings. John’s been working in Nashville for years as a session bass player, and  has a very nice studio. I only wanted his general impression, but he went the extra mile and set up a quick A/B test during a recent session. Here’s what he had to say:

First off WOW, thanks for some toys to play with! Here’s what I’ve got so far:Did a session the other day. One song was just these mics out in the room, capsules aligned and secured. You can hear a distict but subtle difference. The mod is much smoother, whereas the stock mic seems to have a significant rise. The other song was a drum corp type of thing, just snare rudaments. Mics placed a few inches over the head, inch or two inside the hoop. I much prefer the mod, though if you need something hyped for top end, the stock mic might be the better one to go to. The mod is smoother, not brassy. Preamps were Yamaha, very neutral. No compression, straight to my SSL AD, 44k 24bit.

The snare mic setup at John’s studio. John Billings photo

I’ve been meaning to upgrade my WordPress account for quite awhile now, but John’s efforts gave me the final push. Now I can post these files here so you can hear the results and judge for yourself. First, the snare drum solo using the stock, unmodified CM90:

drum corp- Snare 1 N Stock

And next is the modified mic:

drum corp – Snare 1 N Mod

Now the same two mics placed further back as a room mic on a full drum kit. Again the stock mic is the first sample:

Drums Room Nady STOCK

And now the modified mic:

Drums Room Nady MOD

John’s studio is equipped with Genelec monitors, so he’s able to hear things very accurately. I listened to these samples on the best headphones that I have, a pair of  AKG 271s, and on my KRK Rokit 6 studio monitors as well. I noticed a slight drop in level on the modified track, and raising this a touch in Mixbus gives more closely-matched tracks in terms of level. (As you probably know, you’ve got to have levels very close when doing A/B comparisons. In blind tests, people always select a source that’s slightly louder as the better track. )

I tend to agree with John. I’m hearing an overall improvement in freq range, with a touch less upper-midrange and an increase in overall smoothness. It’s a subtle improvement… but when comparing them side-by-side, it’s noticeable.

But something that I always find surprising is the fact that really, these mics aren’t all that horrible right out of the box. I’m showing my age here, but in my studio days you couldn’t even approach this kind of signal for less than three or four C-notes. Sure, the quality control isn’t there… for example, the tiny screws that hold the mic body in place are chewed up and look like they were forced together at the factory… but I can’t really complain given the list price.

In order to make some proper mic comparisons, I’m going to have to buy a proper reference mic, so I’m currently selling some excess gear to buy a Neumann KM184. I’d rather have a vintage KM84, but they’re just much for my current budget to bear…maybe someday. And I’m also on the hunt for an affordable BV107 (or perhaps a suitable equivalent) mic transformer… I want to experiment with a transformer-balanced version of the above mod.